U.S. patent application number 12/181402 was filed with the patent office on 2008-11-20 for nitride single crystal manufacturing apparatus.
This patent application is currently assigned to NGK Insulators, Ltd.. Invention is credited to Makoto Iwai, Fumio Kawamura, Yusuke Mori, Takatomo Sasaki, Takanao Shimodaira, Shiro Yamasaki.
Application Number | 20080282971 12/181402 |
Document ID | / |
Family ID | 38522524 |
Filed Date | 2008-11-20 |
United States Patent
Application |
20080282971 |
Kind Code |
A1 |
Iwai; Makoto ; et
al. |
November 20, 2008 |
NITRIDE SINGLE CRYSTAL MANUFACTURING APPARATUS
Abstract
The apparatus has a crucible for storing a solution; an inner
container 16 for storing a crucible; a heating container 31 for
storing the inner container 16, the heating container 31 including
heating elements 14, a container body 13 provided with the heating
elements 14 and a lid 12 combined with the container body 13; and a
pressure vessel 30 for storing the heating container 31 and for
charging an atmosphere comprising at least nitrogen gas. The lid 12
has a fitting surface 12b to the container body inclined to a
horizontal plane P.
Inventors: |
Iwai; Makoto; (Kasugai-City,
JP) ; Shimodaira; Takanao; (Nagoya-City, JP) ;
Sasaki; Takatomo; (Suita-City, JP) ; Mori;
Yusuke; (Suita-City, JP) ; Kawamura; Fumio;
(Suita-City, JP) ; Yamasaki; Shiro;
(Nishikasugai-Gun, JP) |
Correspondence
Address: |
BURR & BROWN
PO BOX 7068
SYRACUSE
NY
13261-7068
US
|
Assignee: |
NGK Insulators, Ltd.
Nagoya-City
JP
Osaka University
Suita-City
JP
Toyoda Gosei Co., Ltd.
Nishikasugai-Gun
JP
|
Family ID: |
38522524 |
Appl. No.: |
12/181402 |
Filed: |
July 29, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/JP2007/055788 |
Mar 14, 2007 |
|
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12181402 |
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Current U.S.
Class: |
117/206 |
Current CPC
Class: |
C30B 35/002 20130101;
C30B 19/06 20130101; Y10T 117/1096 20150115; C30B 19/02 20130101;
C30B 29/406 20130101; Y10T 117/10 20150115; C30B 9/10 20130101;
Y10T 117/1064 20150115; Y10S 117/90 20130101; Y10T 117/1016
20150115; C30B 7/00 20130101; Y10T 117/1024 20150115 |
Class at
Publication: |
117/206 |
International
Class: |
C30B 7/00 20060101
C30B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 2006 |
JP |
2006-080126 |
Claims
1. A production apparatus for growing a nitride single crystal
using a solution containing a flux and a raw material, said
apparatus comprising: a crucible for storing the solution; an inner
container for storing the crucible; a heating container for storing
the inner container, the heating container comprising a heating
element, a container body equipped with the heating element and a
lid fitted to the container body; and a pressure vessel for storing
the heating container and charging an atmosphere comprising at
least nitrogen gas, wherein the lid has a fitting surface fitted to
the container body and inclined to a horizontal plane.
2. A production apparatus for growing a nitride single crystal
using a solution containing a flux and a raw material, said
apparatus comprising: a crucible for storing the solution; an inner
container for storing the crucible; a heating container for storing
the inner container, the heating container comprising a heating
element, a container body equipped with the heating element and a
lid fitted to the container body; a pressure vessel for storing the
heating container and charging an atmosphere comprising at least
nitrogen gas; and a support member for supporting the inner
container above the container body wherein the support member, the
heating container and the inner container together define a
substantially closed space, and wherein at least one heating
element is provided below the closed space.
3. A production apparatus for growing a nitride single crystal
using a solution containing a flux and a raw material, said
apparatus comprising: a crucible for storing the solution; an inner
container for storing the crucible; a heating container for storing
the inner container, the heating container comprising a heating
element, a container body equipped with the heating element and a
lid fitted to the container body; a pressure vessel for storing the
heating container and charging an atmosphere containing at least
nitrogen gas; and energizing means for energizing the lid toward
the container body from the pressure vessel side.
4. A production apparatus for growing a nitride single crystal
using a solution containing a flux and a raw material, said
apparatus comprising: a crucible for storing the solution; an inner
container for storing the crucible; a heating container for storing
the inner container, the heating container comprising a heating
element, a container body equipped with the heating element and a
lid fitted to the container body; a pressure vessel for storing the
heating container and charging an atmosphere containing at least
nitrogen gas; and a tubular heat insulating member provided between
an outer wall surface of the heating container and an inner wall
surface of the pressure vessel.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method and apparatus for
producing a nitride single crystal using Na flux or the like.
BACKGROUND ARTS
[0002] Gallium nitride-based III-V nitride, which is attracting
attention as an excellent blue light emitting element, is put into
practical use in light emitting diode field, and expected also as a
light pick-up blue-violet semiconductor laser element. In a process
for growing a gallium nitride single crystal by Na flux method, a
mixed gas of nitrogen and ammonia is used with an atmospheric
pressure of 10 to 100 atoms, for example, in Japanese Patent
Publication No. 2002-293696A. In Japanese Patent Publication No.
2003-292400A, also, the atmospheric pressure during the growth is
100 atm or less, with 2, 3, and 5 MPa (about 20 atm, 30 atm and 50
atm) being used in the working examples thereof.
[0003] On the other hand, the applicant disclosed a method for
efficiently growing a gallium nitride single crystal under a
specific condition by use of a hot isostatic pressing (HIP)
apparatus in Japanese Patent Application No. 2004-103093 (WO
2005/095682 A1).
[0004] It is described in "Growth of Large/Low-Dislocation GaN
Single Crystal by LPE Growth" by Kawamura et al. in "Journal of
Japanese Association for Crystal Growth" Vol. 32, No. 1, 2005 that
when a GaN single crystal is grown by Na flux method, the GaN
single crystal is susceptible to blackening due to existence of
nitrogen defects.
[0005] It is also described in Japanese Patent Publication No.
2005-132663A that in growth of a nitride single crystal in a flux
containing lithium, a reaction vessel which contacts with the flux
is formed of metallic tantalum to thereby prevent breakage of the
reaction vessel.
DISCLOSURE OF THE INVENTION
[0006] However, it is proved that the crystal growth by such flux
method using heating and pressurizing apparatuses involves the
following problems. Namely it is extremely difficult to retain the
uniformity of temperature within a furnace in actual growth of
nitride single crystal in an industrial scale, and this may cause
an uneven growing state of crystal or an increased rate of
defectives.
[0007] The present invention thus has an object to prevent, in
growth of nitride single crystal within a furnace by flux method,
the unevenness in growing state of the nitride single crystal and
the increase in rate of defectives resulting from a difference in
temperature within the furnace.
[0008] A first aspect of the invention provides an apparatus for
growing a nitride single crystal using a solution containing a flux
and a raw material, said apparatus comprising:
[0009] a crucible for storing the solution;
[0010] an inner container for storing the crucible;
[0011] a heating container for storing the inner container, the
heating container comprising a heating element, a container body
equipped with the heating element and a lid fitted to the container
body; and
[0012] a pressure vessel for storing the heating container and
charging an atmosphere containing at least nitrogen gas, wherein
the fitting surface of the lid to the container body is inclined to
a horizontal plane.
[0013] A second aspect of the invention provides an apparatus for
growing a nitride single crystal using a solution containing a flux
and a raw material, said apparatus comprising:
[0014] a crucible for storing the solution;
[0015] an inner container for storing the crucible;
[0016] a heating container for storing the inner container, the
heating container including a heating element, a container body
equipped with the heating element and a lid fitted to the container
body;
[0017] a pressure vessel for storing the heating container and
charging an atmosphere containing at least nitrogen gas; and
[0018] a support member for supporting the inner container above
the container body wherein a closed space is formed by the support
member, the heating container and the inner container, and wherein
at least one of the heating element faces the closed space.
[0019] A third aspect of the invention provides an apparatus for
growing a nitride single crystal using a solution containing a flux
and a raw material, said apparatus comprising:
[0020] a crucible for storing the solution;
[0021] an inner container for storing the crucible;
[0022] a heating container for storing the inner container, the
heating container including a heating element, a container body
equipped with the heating element and a lid fitted to the container
body;
[0023] a pressure vessel for storing the heating container and
charging an atmosphere containing at least nitrogen gas; and
[0024] energizing means for energizing the lid toward the container
body from the pressure vessel side.
[0025] A fourth aspect of the invention provides an apparatus for
growing a nitride single crystal using a solution containing a flux
and a raw material, said apparatus comprising:
[0026] a crucible for storing the solution;
[0027] an inner container for storing the crucible;
[0028] a heating container for storing the inner container, the
heating container including a heating element, a container body
equipped with the heating element and a lid fitted to the container
body;
[0029] a pressure vessel for storing the heating container and
charging an atmosphere containing at least nitrogen gas; and
[0030] a cylindrical heat insulating member provided between an
outer wall surface of the heating container and an inner wall
surface of the pressure vessel.
[0031] According to the first aspect of the invention, the inner
container containing the crucible is placed within the heating
container. The heating container includes the heating element, the
container body provided with the heating element, and the lid
combined with the container body By inclining the fitting surfaces
of the container body and the lid to the horizontal plane, the hot
atmosphere within the heating container is prevented from escaping
along the fitting surfaces of the container body and the lid. The
temperature gradient within the inner container can be thus reduced
even in a high-temperature pressurizing condition for growing the
nitride single crystal. Consequently the quality of the single
crystal can be improved to reduce the defectives.
[0032] According to the second aspect of the invention, the closed
space is formed by the support member, the heating container and
the inner container inside the heating container, and at least one
of the heating elements is provided below the closed space.
According to such structure, heat can be directly supplied upwardly
to the closed space from the heater to replenish the heat escaping
upward within the heating container from the closed space side. The
temperature gradient within the heating container and also within
the inner container can be further reduced. Consequently the
quality of the single crystal can be improved to reduce the
defectives.
[0033] According to the third aspect of the invention, the
energizing means is provided for energizing the lid of the heating
container toward the container body from the pressure vessel side.
The hot atmosphere within the heating container can be prevented
from escaping along the fitting surfaces of the container body and
the lid, so that the temperature gradient within the inner
container can be thus reduced even in a high-temperature
pressurizing condition for growing the nitride single crystal.
Consequently the quality of the single crystal can be improved to
reduce the defectives.
[0034] According to the fourth aspect of the invention, by
providing the tubular heat insulating member between the outer wall
surface of the heating container and the inner wall surface of the
pressure vessel, the difference in temperature by thermal
convection can suppressed. The temperature gradient within the
inner container can be thus reduced even under a high-temperature
pressurizing condition for growing the nitride single crystal.
Consequently the quality of the single crystal can be improved to
reduce the defectives.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a schematic view of a growth apparatus according
to the present invention.
[0036] FIG. 2 is a schematic view of a growth apparatus as a
reference example.
[0037] FIG. 3 is a schematic sectional view of a crucible 1, which
shows the growing state of a single crystal 8 within the crucible
1.
BEST MODES FOR CARRYING OUT THE INVENTION
[0038] The present invention will be further described in detail
according to each of the first to fourth embodiments.
[0039] FIG. 1 schematically shows an apparatus for executing the
present invention. FIG. 2 schematically shows an apparatus as a
reference example.
[0040] A pressure vessel 30 comprises a main body 4 and a lid 2.
The lid 2 includes a projection 2a protruded to the inside. A
heating container 31 is set in an internal space 5 of the vessel
30. The heating container 31 comprises a lid 12 and a container
body 13. Each of the container body 13 and the lid 12 is at least
partially formed of a furnace material. In this embodiment, a
series of heating elements 14 are provided so as to face the inside
surface of the container body 13. A heating element 19 is provided
on a bottom plate part 20 of the container body 13.
[0041] In this embodiment, the lid 12 includes a flange part 12a,
and a fitting surface 12b of the lid 12 is inclined at an angle
.theta. to a horizontal plane P. A fitting surface 13a of the
container body 13, which is to abut on the fitting surface 12a, is
inclined also at the angle .theta. to the horizontal plane P. The
fitting surface 12b is inclined to lower toward the outside in a
view from the center of the container body.
[0042] A cylindrical heat insulating members 11 are set between an
outer wall surface 31a of the heating container 31 and an inner
wall surface 30a of the pressure vessel 30. The heat insulating
members 11 are vertically extended substantially over the whole
height of the internal space 5. Energizing means 3 is provided
between the projection 2a of the lid 2 and the upper surface of the
lid 12, so that the lid 12 is energized toward the container body
13 by the energizing means 3.
[0043] An inner container 16 is set within an internal space 15 of
the heating container 31. The inner container 16 is supported above
the bottom plate part 20 of the container body of the heating
container 31 through support members 17, with the bottom surface of
the inner container 16 being in contact with the upper ends of the
support members 17. The support members 17 have, for example, a
cylindrical shape, and a substantially closed space 18 is formed by
the bottom plate part 20, the support members 17 and the inner
container 16. The heating element 19 mounted on the bottom plate
part 20 faces the closed space 18.
[0044] A crucible 1, for example, shown in FIG. 3 is set within the
inner container 16, and a seed crystal 6 is immersed in a solution
7 produced within the crucible 1.
[0045] A mixed gas cylinder not shown is provided outside the
pressure vessel 30. The mixed gas cylinder is filled with a mixed
gas having a predetermined composition, and the mixed gas is
compressed to a predetermined pressure by a compressor, and
supplied into the pressure vessel 30 through a supply pipe not
shown. Of this atmosphere, nitrogen is used as a nitrogen source,
and an inert gas such as argon suppresses vaporization of flux such
as sodium. The pressure of the atmosphere is monitored by a
pressure gauge not shown.
[0046] When the heating elements 14 and 19 are heated, and the
pressure vessel 30 is internally heated and pressurized by carrying
nitrogen gas thereto, mixed raw materials are entirely dissolved
within the crucible 1 to form the solution 7, as shown in FIG. 3.
If a predetermined single crystal growth condition is retained, a
single crystal 8 is grown on the seed crystal 6 with stable supply
of nitrogen into the growing raw material solution 7 as shown by
arrow B.
[0047] FIG. 2 schematically shows an apparatus as a reference
example.
[0048] A pressure vessel 30 comprises a main body 4 and a lid 2. A
heating container 31 is set in an internal space 5 of the vessel
30. The heating container 31 comprises a lid 21 and a container
body 22. In this example, a series of heating elements 14 are
provided so as to face the inside surface of the container body 22.
A heating element 19 is provided on a bottom plate part 20 of the
container body 13.
[0049] An inner container 16 is set within an internal space 15 of
the heating container 31. The inner container 16 is supported above
the bottom plate part 20 of the container body of the heating
container 31 through a plurality of support legs 27, with the
bottom surface of the inner container 16 being in contact with the
upper ends of the support legs 27. Three or more support legs 27
are provided and disposed adjacently each through a clearance.
Therefore, no closed space is formed by the bottom plate part 20,
the support legs 27 and the inner container 16. Namely a space 28
on the inside of the support legs communicates with the internal
space 15 of the heating container 31.
[0050] A crucible 1, for example, shown in FIG. 3, is set within
the inner container 16, and a seed crystal 6 is immersed in a
solution 7 produced within the crucible 1.
[0051] In the embodiment of FIG. 1, the hot atmosphere within the
heating container 31 can be prevented from escaping along the
fitting surfaces of the container body 13 and the lid 12 by
inclining the fitting surfaces 12b and 13a of the container body 13
and the lid 12 by the angle .theta. to the horizontal plane P. Such
hot atmosphere tends to collect on the lower side of the lid 12 due
to the specific gravity difference, and is hardly discharged out of
the container body 13. In the apparatus shown in FIG. 2, the hot
atmosphere tends to horizontally flow and discharge out along
fitting surfaces 21a and 22a of the lid 21 and the container body
22. Consequently the heat transfer from down to up is easily
promoted within the heating container 31, causing a temperature
difference within the internal space 15.
[0052] The angle .theta. of the fitting surfaces 12b and 13a to the
horizontal plane P is set preferably to 45.degree. or more, from
the viewpoint of the above-mentioned action and function of the
present invention, more preferably to 60.degree. or more. By
extending the fitting surface 12b, the pathway of the atmosphere to
leak can be extended. The upper limit of .theta. is not
particularly limited. However, since an excessively large .theta.
makes the handling difficult, the angle .theta. is set preferably
to 85.degree. or less, more preferably to 80.degree. or less.
[0053] In the embodiment of FIG. 1, the substantially closed space
18 is formed by the support members 17, the heating container 31
and the inner container 16 inside the heating container 31, and at
least one heating element 19 is provided below the closed space 18.
According to this, the heat from the heater 19 can be directly
supplied into the closed space 18 to replenish the heat escaping
upward within the heating container 31 from the lower side of the
closed space 18, to thereby further reduce the temperature gradient
within the heating container 31 and also within the inner container
16. Consequently the quality of the single crystal can be improved
to reduce the defectives.
[0054] The shape of the support member 17 is not particularly
limited as long as it can form such a closed space. Although the
support members 17 are needed to have a some tube-like shape for
forming the closed space, it may have a cross sectional shape such
as perfect circle, ellipse, race track-like shape, triangle, or
quadrangle without any limitation.
[0055] The closed space does not have to be perfectly sealed to the
vessel internal space 15, but just has to be substantially closed.
For example, the support members 17 can include a cutout or
through-hole.
[0056] The heating element 19 just has to be located below the
lower side of the closed space 18. For example, the heating element
may be buried in the furnace material constituting the bottom plate
part 20, or be exposed to the surface of the bottom plate part
20.
[0057] In this embodiment, the energizing means 3 is provided for
energizing the lid 12 of the heating container 31 toward the
container body 13 from the pressure vessel 30 side. According to
this, the hot atmosphere within the heating container 31 can be
prevented from escaping along the fitting surfaces of the container
body 13 and the lid 12, and the temperature gradient within the
inner container 16 can be thus reduced even under a
high-temperature pressurizing condition for growing the nitride
single crystal. Consequently the quality of the single crystal can
be improved to reduce the defectives.
[0058] The energizing means is never particularly limited, and may
be a metallic spring such as coil spring or plate spring.
Otherwise, energizing means such as snap lock or weight can be
used. The energizing means does not need heat resistance since it
is not subjected to so much high temperature (generally 200.degree.
C. or lower).
[0059] In this embodiment, by providing the tubular heat insulating
member 11 between the outer wall surface of the heating container
31 and the inner wall surface of the pressure vessel 30, the
thermal convection is limited to suppress the temperature
difference resulting from the convection. Accordingly the
temperature gradient within the inner container can be reduced even
in a high-temperature pressurizing condition for growing the
nitride single crystal. Consequently the quality of the single
crystal can be improved to reduce the defectives.
[0060] The concrete shape of the tubular heat insulating members 11
is not particularly limited. The tubular heat insulating members
can have, for example, a cross sectional shape such as perfect
circle, ellipse, race track-shape, triangle or quadrangle.
[0061] In the present invention, as the furnace material, for
example, high alumina refractory brick (Isolite, ISO-COR (trade
names), graphitic refractory (GRAFSHIELD.TM.), and hollow
spherulitic fused alumina (alumina bubble) can be used, although
the furnace material is not particularly limited thereto.
[0062] In the present invention, as the material of the heating
element, for example, tantalum, SiC, SiC-coated graphite, nichrome,
and Kanthal Super.TM. can be used although it is not particularly
limited thereto.
[0063] In the present invention, as the material of the support
members for supporting the inner container, for example, SUS 310S,
Inconel, tantalum, molybdenum, and tungsten can be used although it
is not particularly limited thereto.
[0064] In the present invention, a thickness T of the lid 12 of the
heating container is set preferably to 70 mm or more, from the
viewpoint of reducing the temperature gradient during growth within
the heating container, more preferably to 100 mm or more.
[0065] In the present invention, the material of the tubular heat
insulating members provided between the heating container and the
pressure vessel is not particularly limited, and examples thereof
include SUS 304, aluminum, quartz glass, and Pyrex glass. The
tubular heat insulating members just have to be heat resistant to,
for example, 200.degree. C. or higher since it is not subjected to
so much high temperature. For restricting the thermal convection of
the high-temperature and high-pressure gas leaked out of the
heating container, the space from the heating container is set
preferably to be smaller than 5 cm. A plurality of tubular heat
resisting members may be set.
[0066] A thickness t of the tubular heat insulating member is set
preferably to 0.5 mm or more, from the point of the gist of the
invention, more preferably to 1 mm or more, although it is not
particularly limited.
[0067] Examples of the seal member between the lid of the heating
container and the container body include ceramic fiber, ceramic
wool, graphite wool and steel wool.
[0068] In the present invention, the growth of the single crystal
is performed in an atmosphere containing nitrogen. The nitrogenous
atmosphere may be composed only of nitrogen, but can include a
non-oxidizing gas other than nitrogen, for example, an inert gas
such as argon or a reductive gas.
[0069] In the present invention, the device for heating the raw
material mixture to produce the solution in the single crystal
growth apparatus is not particularly limited. Although a hot
isostatic pressing apparatus is preferred as such device, other
atmospheric pressurizing type heating furnaces are also usable.
[0070] The flux for producing the solution is not particularly
limited, but it is preferably composed of one or more metals
selected from the group consisting of alkali metals and alkali
earth metals, or alloys thereof. As such metals, sodium, lithium
and calcium are particularly preferred, and sodium is most
preferred.
[0071] As materials other than the flux and single crystal raw
material to be added to the raw material mixture, for example,
potassium, rubidium, cesium, magnesium, strontium, barium and tin
can be given.
[0072] As a dopant, a small amount of impurity element can be
added. For example, silicon can be added as n-type dopant.
[0073] By the growing method according to the present invention,
for example, the following single crystals can be suitably grown:
GaN, AlN, InN, mixed crystal thereof (AlGaInN), and BN
[0074] The heating temperature and pressure in the single crystal
growing process are not particularly limited since they are
selected depending on the kind of single crystal to be grown. The
heating temperature can be set, for example, to 800 to 1500.degree.
C. The pressure is not particularly limited either, but is
preferably set to 1 MPa or more, more preferably to 5 MPa or more.
The upper limit of the pressure is not particularly regulated, but
can be set, for example, to 200 MPa or less.
[0075] The material of the crucible for performing the reaction is
not particularly limited, and the crucible may be formed of an
airtight material having durability under an intended heating and
pressurizing condition. Examples of such material include
high-melting point metals such as metallic tantalum, tungsten and
molybdenum, oxides such as alumina, sapphire and yttria, nitride
ceramics such as aluminum nitride, titanium nitride, zirconium
nitride and boron nitride, carbides of high-melting point metals
such as tungsten carbide and tantalum carbide, and thermal
decomposition products such as p-BN (pyrolytic BN) and p-Gr
(pyrolytic graphite).
[0076] Further concrete single crystals and growing procedures
thereof will be then described.
(Growth Example of Gallium Nitride Single Crystal)
[0077] The present invention can be used to grow gallium nitride
single crystal using a flux containing at least sodium metal. A
gallium raw material is mixed to the flux. As the gallium raw
material, gallium single metal, a gallium alloy and a gallium
compound are applicable, and gallium single metal is suitably used
from the viewpoint of handling.
[0078] The flux can include a metal other than sodium, for example,
lithium. Although the gallium raw material and the flux raw
material such as sodium may be used in an appropriate proportion,
excess use of Na is generally considered. This is, of course, not
limitative.
[0079] In this embodiment, the growth of gallium nitride single
crystal is carried out under an atmosphere consisting of a mixed
gas containing nitrogen gas at a total pressure ranging from 300
atm to 2000 atm. By setting the total pressure to 300 atm or more,
gallium nitride single crystal of good quality could be grown, for
example, in a high-temperature range of 900.degree. C. or higher,
more preferably in a high-temperature range of 950.degree. C. or
higher. This reason is not known exactly but this is attributable
to that the nitrogen solubility is increased according to
temperature rise, and nitrogen efficiently dissolves in the growing
solution. When the total pressure of the atmosphere is set to 2000
atm or more, the density of the high-pressure gas significantly
gets close to that of the growing solution, so that it becomes
difficult to retain the growing solution within the vessel for
performing the reaction of the growing solution.
TABLE-US-00001 TABLE 1 Densities of various materials (g/cm.sup.3)
Sodium metal Nitrogen Argon 800.degree. C. 1 atm 0.75 0.0003 0.0004
927.degree. C. 300 atm 0.08 01 927.degree. C. 1000 atm 0.21 0.33
927.degree. C. 2000 atm 0.3 0.5 (estimation) (estimation)
[0080] In a preferred embodiment, the nitrogen partial pressure in
the atmosphere during growth is set to 100 atm or more and 2000 atm
or less. By setting the nitrogen partial pressure to 100 atm or
more, gallium nitride single crystal of good quality could be grown
in a high-temperature range of, for example, 1000.degree. C. or
higher while promoting the dissolution of nitrogen to the flux.
From this viewpoint, the nitrogen partial pressure is set more
preferably to 200 atm or more. The nitrogen partial pressure is set
also preferably to 1000 atm or less from the practical point of
view.
[0081] Although the gas other than nitrogen in the atmosphere is
not particularly limited, an inert gas is preferred, and argon,
helium or neon is particularly preferred. The partial pressure of
the gas other than nitrogen corresponds to a value obtained by
subtracting the nitrogen gas partial pressure from the total
pressure.
[0082] In a preferred embodiment, the growth temperature of gallium
nitride single crystal is set to 950.degree. C. or higher, more
preferably to 1000.degree. C. or higher, and even in such a
high-temperature range, gallium nitride single crystal of good
quality can be grown. The growth at increased temperature and
increased pressure can probably improve the productivity.
[0083] Although the upper limit of the growth temperature of
gallium nitride single crystal is not particularly limited, an
excessively high growth temperature makes the crystal growth
difficult. Therefore, the growth temperature is set preferably to
1500.degree. C. or lower. From this viewpoint, the temperature is
set more preferably to 1200.degree. C. or lower.
[0084] As the material of the growth substrate for epitaxially
growing the gallium nitride crystal, sapphire, AlN template, GaN
template, self-standing GaN substrate, silicon single crystal, SiC
single crystal, MgO single crystal, spinel (MgAl.sub.2O.sub.4), and
perovskite composite oxide such as LiAlO.sub.2, LiGaO.sub.2,
LaAlO.sub.3, LaGaO.sub.3 or NdGaO.sub.3 can be given although it is
not particularly limited thereto. A cubic perovskite composite
oxide represented by the composition formula
[A.sub.1-y(Sr.sub.1-xBa.sub.x).sub.y]
[(Al.sub.1-zGa.sub.z).sub.1-uDu]O.sub.3 (wherein A is a rare earth
element; D is one or more elements selected from the group
consisting of niobium and tantalum; y=0.3 to 0.98; x=0 to 1; z=0 to
1; u=0.15 to 0.49; and x+z=0.1 to 2) is also usable. Further, SCAM
(ScAlMgO.sub.4) is also usable.
(Growth Example of Aln Single Crystal)
[0085] The present invention could be confirmed to be effective for
growth of AlN single crystal by pressurizing a melt including a
flux containing at least aluminum and alkali earth metal in a
specific condition under a nitrogen gas containing atmosphere.
EXAMPLES
Example 1
[0086] The apparatus schematically shown in FIG. 1 was used to
carry out growth of gallium nitride single crystal.
[0087] Concretely the support members 17 were formed, using SUS
310S, into a cylindrical shape having a diameter .phi. of 155 cm
and a height of 10 cm. Six holes 3 cm in diameter were equally
provided on the side surface of the cylindrical support members
17.
[0088] As the energizing means 3, four coil springs 3 made of
spring steel and having a spring rate of 2 kg/mm were used. The
heat insulating members 11 were formed, using stainless (SUS 304),
into a cylindrical shape. A thickness of the heat insulating
members 11 was 1 mm. The distance between each of the cylindrical
heat insulating members and the furnace material was 2 cm, and the
distance between each of the cylindrical heat insulating members
and the pressure vessel 30 was about 4 cm.
[0089] In the lid 12, the angle .theta. was 60.degree., and the
height of the flange part 2a was 10 cm. A thickness of the lid 12
was 15 cm. The inner container 16 had a diameter of 180 mm and a
height of 15 cm.
[0090] Using this growth apparatus, temperature distribution in the
heating container was measured at internal temperature and pressure
of 900.degree. C. and 5 MPa. Consequently the diameter directional
temperature distribution was .+-.2.degree. C., and the vertical
temperature distribution was +3.degree. C.
[0091] The growth of GaN single crystal was carried out using this
apparatus. Concretely metal Na 90 g, metal Ga 100 g and metal
L.+-.130 mg were weighted within a globe box. The metal Ga and
metal Li were enclosed by the metal Na. These raw materials were
charged in an alumina-made crucible 1 with inside diameter of 70
mm. As the seed crystal 6, an AlN template substrate, GaN template
substrate or self-standing GaN single crystal substrate with .phi.
2 inches was used. The substrate was horizontally disposed on the
bottom of the crucible 1 so that the single crystal thin film of
the template was upward, or the Ga surface of the self-standing GaN
single crystal substrate was upward. The AlN template substrate is
a substrate obtained by epitaxially growing an AlN single crystal
thin film on a sapphire substrate in a thickness of 1 micron, and
the GaN template substrate is a substrate obtained by epitaxially
growing a GaN single crystal thin film on a sapphire substrate in a
thickness of 3 microns.
[0092] The pressure vessel 30 was evacuated to vacuum by a vacuum
pump for removing the atmosphere within the vessel, gas-substituted
by nitrogen gas, raised in temperature and pressure to 900.degree.
C. and 50 atm over one hour, and then retained at 900.degree. C.
for 100 hours. After naturally allowed to cool to room temperature,
the crucible was taken out of the growth apparatus, and treated in
ethanol to dissolve Na and Li. Thereafter, the remaining Ga was
removed by dipping in diluted hydrochloric acid to take out the
resulting GaN single crystal. The GaN single crystal had a
substantially circular shape with a grain size of .phi. 2 inches
and a thickness of about 5 mm. The crystal was substantially
colorless and transparent.
Comparative Example 1
[0093] An apparatus as shown in FIG. 2 was manufactured, in which
four alumina pipes were set as the support members 27, but the
energizing means 3 and the heat insulating members 11 were not
provided. As a result of temperature distribution measurement, the
temperature within the heating container was distributed so as to
become higher toward the top, with a temperature gradient of
50.degree. C. per 10 cm-height in vertical view.
[0094] The same growth of GaN single crystal as in Example 1 was
carried out using this apparatus. As a result, single crystal of
good quality could not be grown.
[0095] While specific preferred embodiments have been shown and
described, the present invention is never limited by these specific
embodiments, and can be carried out with various modifications and
substitutions without departing from the spirit and scope of the
claims of the present invention.
* * * * *